Total Rewards is nationwide, Mlife is mainly Las Vegas based (and a few other casinos). [I'm NYC based, and Atlantic City (which has 4 TR casinos), make this system best for me.]
Harrahs casinos have Diamond Lounges (and in AC 2 Seven Stars)--MLife casinos don't (at least they didn't, when I played there last) have "top tier" lounges.
To be honest I don't have much interest currently in TR's other properties. So it doesn't fit into my decision very much. And lounge is a nice throw in but not really needed. I'm still not sure where to devote my energy. I think more research is needed.